Resonance Raman Spectroscopy at 257 nm Excitation of Normal and Malignant Cultured Breast and Cervical Cells

Abstract

The sensitivity and selectivity of UV-excited resonance Raman spectroscopy indicate that this technique may be useful in studying certain biochemical changes in cells, especially changes in DNA that occur during the development of cancer. To determine whether this technique can distinguish normal from malignant cells, we have measured UV resonance Raman spectra at 257.26 nm excitation of suspensions of normal and malignant cultured breast and cervical cells. Samples were excited with the use of an intracavity doubled argon-ion laser, and the spectra were recorded with a single grating spectrograph and a liquid nitrogen-cooled charge-coupled device. Cell spectra obtained closely resembled that of DNA, with peaks around 1330, 1480, and 1580 cm⁻¹, due to the nucleotide bases. In addition to these, the uracil base in RNA provides a peak at 1230 cm⁻¹. Strong tryptophan and tyrosine contributions appear in the 1520–1670 cm⁻¹ range. The ratios of Raman spectral peaks 1480/1614 cm⁻¹ and 1480/1540 cm⁻¹, which are sensitive to the concentration of nucleic acids relative to cell proteins, were found to be higher in malignant cells than in normal cells. Normal and malignant cells could also be differentiated by using the ratio at 1330/1480 cm⁻¹. This difference may be the result of decreased hypochromism due to changes in stacking of the purine bases. Changes in relative amounts of RNA may also contribute to this ratio. The results of this pilot study indicate that there may be significant differences in the UV resonance Raman spectra of normal and cancerous cells. These differences may be related to changes in nucleotide/protein concentrations in the cell, as well as changes in the vibrational structure of the nucleic acids associated with the malignant cell phenotype.